The invention relates to a weight regulator for an injection-moulding machine to be controlled by a process regulator and comprising a circuit arrangement for determining a value for the final pressure adjustment from a predetermined nominal weight of the injection-moulded parts to be produced by the injection-moulding machine.
The book "Prozessautomatisierung beim Extrudieren und Spritzgiessen von Kunststoffen" by Dr. Ing. H. G. Wiegand, Carl-Hansen-Verlag Munchen-Wien 1979, p. 179-185 discloses a process regulation system for a controllable injection-moulding machine comprising a circuit arrangement in the form of a micro-computer, to which is supplied a quantity corresponding to the nominal weight of an injection-moulded part and from which there is calculated, with the aid of model equations, a pressure profile for the final pressure phase of the injection-moulding machine. This pressure profile is supplied to a final pressure control circuit of the injection-moulding machine as a nominal value, as a result of which the weight of the injection-moulded part is adjustable by way of the final pressure. With the aid of model equations, the pressure profile is calculated from a predetermined nominal weight only on approximation, however, because changes of the injection-moulding material occurring during the production or disturbances in the injection-moulding machine cannot be taken into account with the use of mode equations, which are fed into the microcomputer before the beginning of the production and then remain unchanged. As a result, permanent deviations of the actual weight from the adjusted nominal weight of the injection-moulded parts are obtained.